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Lens shift question

post #1 of 9
Thread Starter 
If I mount my 137.7 diagonal screen on a wall at the top of my ceiling and then mount my JVC RS35 projector on the ceiling so that its at the top of the screen about 20 feet away, but there is a large wood beam about 5 feet in front of the projector running across the room that hangs about 10 inches from the ceiling, I assume that the image will still project onto the full screen due to lens shift and not onto the beam? Sorry if this is confusing.
post #2 of 9
Uh oh, we're not in Kansas anymore Toto.
post #3 of 9
Thread Starter 
hahaha. i also put this in the wrong forum. Can't delete it or move it to projectors.
post #4 of 9
Quote:
Originally Posted by Adz523 View Post

If I mount my 137.7 diagonal screen on a wall at the top of my ceiling and then mount my JVC RS35 projector on the ceiling so that its at the top of the screen about 20 feet away, but there is a large wood beam about 5 feet in front of the projector running across the room that hangs about 10 inches from the ceiling, I assume that the image will still project onto the full screen due to lens shift and not onto the beam? Sorry if this is confusing.

As long as the line of sight from the lens to the top of the screen is clear, then no problem. Did not expect to see a projector question here. By the way, nice projector.
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post #5 of 9
It doesn't sound as if there's line of sight...
post #6 of 9
Thread Starter 
Quote:
Originally Posted by AV Science Sales 5 View Post

As long as the line of sight from the lens to the top of the screen is clear, then no problem. Did not expect to see a projector question here. By the way, nice projector.

Mike -- If I drop the projector down using a 12" pipe so that the lens is firing below the 10" beam, but that darn beam is still about 5-6 feet in front of the projector, would that work?
post #7 of 9
you could just affix a string to the screen wall at the same height as the top edge of the screen , then draw it out to the back of the room... you can determine exactly how much drop you'll need at the projector's location to clear the beam. make sense? btw... painter's tape for no residue on your wall, and mason string doesn't stretch.
post #8 of 9
This sounds like a middle school or high school geometry problem.
A=15ft. The distance from the screen to the beam
B=10". The distance the end of the beam to the ceiling.
X=4A/3. The ratio of the distance the projector is from the screen compared to the beam.

10" * (4/3) = 13.3".

So make sure your lens is 13.3" below the ceiling and you will have line of sight. If however, your screen is not at the meeting point of the wall and ceiling, but is instead a couple inches down, you won't have to have the lens as far down.
post #9 of 9
^^^ Nice job! So, we are in Kansas...
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